1. Field of the Invention
This invention relates to a process for gettering defects in semiconductor devices. The process accomplishes gettering by first scanning a surface of the semiconductor with a laser beam to drive in a dopant and then heating the semiconductor.
2. Description of the Prior Art
During the fabrication of a semiconductor device, such as an integrated circuit, unwanted defects are generated in the bulk of the semiconductor near the active surface region. These defects degrade device performance and reduce yield of acceptable devices. At elevated temperatures defects become more mobile and can travel to regions of high strain field. If a strain field is deliberately created away from the active surface of a device, then, during a high temperature cycle, defects can be trapped there and prevented from interfering with device performance. Among the techniques that have been used to form the requisite strain field has been scanning a laser beam over the back surface (or other "distant" area) to induce lattice damage and strain. That technique has beeen disclosed in U.S. Pat. No. 4,131,487, issued Dec. 26, 1978, to Pearce et al.; U.S. Pat. No. 4,257,827, issued Mar. 24, 1981, to Schwuttke et al.; and Burggraaf, Semiconductor International, Sept., 1980, page 52.
An alternative gettering technique that has been disclosed involves thermal diffusion of dopants into the semiconductor bulk from the back surface, thereby creating lattice distortion. For example, Petroff et al., U.S. Pat. No. 3,997,368, issued Dec. 14, 1976, discloses a process for gettering stacking faults by forming a stressed layer on the back surface of a wafer, preferably preceded by thermally diffusing phosphorus into the back surface.
Although the gettering processes of the prior art are effective to a limited degree, their effectiveness can be impaired by subsequent treatment of the semiconductor device and/or by generation of a concentration of defects greater than that which can effectively be eliminated by their gettering action.
Another process that has been accomplished with lasers is dopant diffusion. In preparing n-type and p-type junctions, dopants that had been deposited or spun on semiconductor wafer surfaces were diffused into the bulk by exposing the wafers to suitable laser beams. This technique has been disclosed by Burggraaf, op. cit., p. 54.